Electrolytic decomposition of alkaline salts.



PATENTED OUT. 20, 1903.

M. WILDERMANN. ELECTROLYTIC DECOMPOSITION OP ALKALINE SALTS.

APPLIOATIONIILED MAY 5, 1902.

7 SHEETS-SHEET 1.

N0 MODEL.

No. 741,864. A PAT NTED 0GT.20,1903..

M. WILDERMANN.

ELECTROLYTIC DECOMPOSITION OF ALKALINE SALTS.

APPLICATION FILED MAY 5, 1902.

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PATENTED OCT. 20, 1903. I M.. WILDERMANN ELECTROLYTIC DECOMPOSITION OF ALKALINE SALTS.

APPLICATION FILED MAY 5, 1902.

7 SHEETS-SHEET a.

N0 MODEL.

' No. 741,864. PATENTED OGT.20,,1903.

M. WILDERMANN.

ELECTROLYTIC DEGOMPOSITION'OF ALKALINE SALTS.

' APPLICATION FILED MAY 5, 1902.

no MODEL. 7 sHBETs-sHEnT 4.

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' PATENTED OCT. 20, 1903.

WILDERMANN.

ELEGTROLYTIG DECOMPOSITION 0P ALKALINE SALTS.

. APPLICATION PILBD MAY 5, 1902.

'1 SHEETS-SHE no MODEL.

No. 741,864. PATENTED OCT. 20, 1903.

M. WILDERMANN. ELECTROLYTIC DECOMPOSITION OI ALKALINE SALTS.

APPLICATION FILED MAY 5. 1902. NO MODEL. 7 SHEETS- SHEET 6.

v 2 52 f I 2 W W No. 741,364. PATENTED OCT. 20, 1903. M. WILDBRMANN.

ELECTROLYTIC DECOMPOSITION OP, ALKALINE SALTS.

Ammonxonrmnnmu 5, 1902. no MODEL. 7 SHBETS-SIEET 7.

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MEYER WILDERMANN, OF LONDON, ENGLAND.

SPEGIEICATION forming part of Letters Patent No. 741,864, dated October 20, 1903. Application filed May 5, 1902. Serial No. 106,02 7. (N0 specimens.)

To all whom it warty concern.-

Be it known that I, MEYER WILDERMANN, chemist, a subject of the Czar of Russia, residing at 10 Elers road, Ealing, London,S.W., England, have invented certain new and useful Improvements in and Relating to the Electrolytic Decomposition of Alkaline Salts, of which the followingis a specification.

My invention relates to cells for the electrolysis of alkaline salts, and more particularly to the improved forms of electrolytic cell described in Patent No. 659,655 and Serial No. 53,275. The cells describedin these specifications consist of a decomposing-compartment separated from a combining-compartment by a partition composed of superim posed troughs containing a quantity of mer: cury which has free surfaces exposed in the decomposing and combining compartments. On passing an electric current through the brine solution to the mercury in the troughs the alkaline metal is deposited on the surface of the mercury in the decomposing-compartment and immediately forms an amalgam therewith. The amalgam then automatically passes through the mercury seal to the combining-compartment, where the alkali metal combines with water to form alkaline hydrate.

In Patent No. 659,655, referred to above, it

is stated that the transference of the amalments had shown that the main factor in effecting this transference of amalgam is the diiferences which occur between the surface tensions of the amalgam and mercury in the troughs. It has since been found, however, that the conditions under which these automatic actions may be utilized are so limited as to be inconvenient and difiicult to maintain in practice. One of the limiting conditions is that the mercury seal in the troughs should not exceed about three millimeters in depth, for at a depth of about four the cellsfor some time there is a tendency for the richer amalgam and especially that at the outer edges of the troughs in the decomposing compartment to thicken,become fluify,

and then even hard, thereby gradually stopping the surface-tension effects and the diifusion of the alkali metal. Solid amalgam then quickly grows on the decomposing-compartment sides of the troughs and eventually breaks themercury seal. Further, with cells in which the circulation is produced by these automatic means only comparativelysmall current densities per unit area of mercury surface must be employed. The greater are the current densities employed the more rapidly will amalgam be formed on the mercury in the decomposing-compartment, and if the amalgam forms there faster than it can be transferred below the rib of the seal to the other side of the trough a hardening of the amalgam will occur and the working of the cell will thus be interrupted.

My invention consists in producing circulation of mercury and amalgam in cells which employ a partition of superimposed troughs containing mercury with free surfaces exposed in the decomposing and combining compartments by stirring and mixing the mercury and amalgam, and thereby causing amalgam to pass below the rib of the seal, whence it rises by its buoyancy to the surface of the mercury in the combining compartment, whereby deep mercury seals and high-current densities may be employed, the rate of transference of alkali metal from the decomposing-compartment to the combining-compartment may be effectively controlled and regulated, and the etiicienoy of the cells greatly improved.

My invention further consists in the improved constructions of circular cells to be hereinafter described.

Referring now to the accompanying drawings, Figure 1 is a sectional side elevation of an electrolytic cell provided with two partitions of longitudinal superimposed mercurytroughs with my invention applied. The section is taken on the line A Aof Fig. 2. Fig. 2 is 'a cross-sectional view of the same on the line B B of Fig. 1. Fig. 3 is a plan of the same. Fig. 4 is a vertical sectional elevation on the center of an electrolytic cell provided with circular "mercury troughs and constructed according to my invention. Fig. 5 is a plan of the same with the cover 71. removed in order that the arrangement of the carbon anodes may be seen. Fig. 6 ma sectional elevation of a modified form of circular cell, and Fig. 7 is a plan of the same. Fig. 8 is a cross-sectional view of'one of the troughs drawn to an enlarged scale.

In carrying my invention into effect, according to one modification, as illustrated in Figs. 1 to 3, I provide a rectangular tank a, preferably lined with sheets of ebonite or other suitable non-conducting material, and I divide the tank into two or more compartments by means of partitions formed by a series of superimposed longitudinal troughs 1) containing mercury. A mercury seal is formed by means of ribs 0 on the under side of the troughs dipping into the mercury in the troughs below. The troughs are constructed of non-conducting material, preferably of iron covered by ebonite or other nonconducting material, and they are supported by non-conducting uprights or end pieces d, fixed to the sides of the cell and provided with recesses to receive the ends of the troughs. The interstices at the ends are filled up in any suitable manner to prevent leakage of the liquid from one compartment into the other. The edges of the bottom troughs are raised a little above the bottom of the cell, so that carbon particles, due to the disintegration of the carbon anodes, may not settle on the surface of the mercury there. The top rib a of the mercury seal is carried by a raised trough e, which forms a water seal with the flange of the coverf over the alkaline-hydrate solution. The carbon anodes g preferably rest on the bottom of the decomposingcompartment, their upper ends projecting through a wood cover h, which is lined inside with a sheet of ebonite. The cover carries flanges i of ebonite to form a water seal with the water-troughs m m, whereby the escape of the chlorin evolved when the cell is in operation is prevented. The upper ends of the carbons enter and are in electrical contact with a metallic frame 0, to which the positive terminal or is fixed. (See Fig. 3.) The negative terminal 19 is fixed to a metallic strip q, secured outside one side of the cell, opposite the ends of the troughs, and metallic conductors 7", pass from this strip (1 through the wall of the cell into the mercury in the troughs. The current passes from the carbon anodes through the brine solution to the mercury in the troughs and out at the negative terminals. The alkaline-chlorid solution is thus decomposed, the alkali metal being deposited on the mercury to form an amalgam and the chlorin liberated and withdrawn for the manufacture of bleaching-powder. Instead of employing the current connections above referred to I may employ the connections described in Serial No. 53,275. I preferably use a mercury seal in the troughs from seven to ten millimeters deep. This depth considerably exceeds the maximum depth at which automatic diffusion and surface-tension effects produce circulation of amalgam from one side of the troughs to the other. According to my invention I provide means for stirring the mercury and amalgam on the decomposing-compartment side of the trough, so as to deflect the amalgam formed at the surface of the mercury deeply into the mercury and thoroughly agitate and mix the mercury and amalgam, whereby amalgam is transferred under the ribs of the seals to the other sides of the troughs. As the amalgam is lighter than the mercury which is comparatively still in the combining-compartmentsides of the troughs, it immediately rises to the surface of the mer cury. Small pieces of carbon, to which are applied a suitable conductive material independent of the amalgam, are placed on the surfaces of the mercury on the sides of the troughs in the combining compartment. These special carbons may consist of small pieces of carbon j, around which one or more fine pieces of wire have been wound, pieces of electrolytically-coated carbon, or pieces of a combination of metal filings and carbon, and the vigorous local action set up between them causes a-ra'pid decomposition of the amalgam and combination of the alkali metal with the water in the combining-compartment, the liberated hydrogen being led away for use as required. It is well known, of course, that if a moistened zinc and carbon plate be in metallic contact galvanic action takes place. By means of the above-described car-- bon pieces j there is produced a number of what might be termed small local deposingcells on the surface of the amalgam in the combining-compartment. The diiference of potential between these carbon particles and the mercury produces an electric current which decomposes the sodium amalgam wherever the carbon particles are placed. The decomposition of the amalgam on account of its contact with the water in the combining compartment is thus greatly assisted. I am thus able to decompose a much greater quantity of amalgam in a given time than would be possible if no such internal assistance were rendered. Consequently the cell may be Worked with very much higher current densities per unit area of mercury surface without any fear of causing an accumulation of amalgam on the combining-compartment sides of the troughs. The stirrers in this modification consist of a series of ebonite blades 5, provided with teeth or projections t, which (lip into the mercury in the decomposingcompartment sides of the troughs. The blades are connected together at their tops and bottoms by cross-ties u, and they are adjustably fixed by means of screwed supporting-rods 00, which may be covered with ebonite, to the cross-bar y, which may be supported by brackets o, secured to the sides of the cell. The lower ends of the blades may be guided by means of small wheels rolling upon beveled guides 1, fixed and extending along the bottom of the cell. The cross-bar carrying the blades is reciprocated, its travel being preferably equal to or somewhat greater than the pitch of the blades, so that the whole surface of the mercury in one side of the trough is disturbed at each'stroke of the bar. In order to prevent the mercury spilling over the edges of the troughs when it is being agitated by the stirrers,l form flanges 2 along the sides of the trough, these flanges being increased in height toward the ends of the troughs, or the ends of the troughs may be covered'by strips of ebonite carried by the troughs above. The stirrers must not travel quite to the ends of the troughs. The mercury will, however, be agitated enough at the ends to prevent hardening of the amalgam there. Any suitable means may be employed to reciprocate the bar. The device shown in Fig. 2 consists of a pivoted lever 2, one end of which engages with two collars or projections 3 on the crossbar 3 its other end being rocked by means of an eccentric keyed to a shaft rotated in any suitable manner. The supporting-rods 0: are passed through a narrow ebonite cover 4., so as to be made gas-tight, the flanges 5 of the cover forming a gas-tight seal with the water-tanks e and m. The decomposing-compartment is provided with the necessary openings 7 and 6 for the'admission of concentrated brine solution and the withdrawal of dilute solution respectively. If desired, the opening 7 may be made large enough for the withdrawal of the chlorin together with the dilute brine solution, or a separate opening may be provided to lead the chlorin away. An additional hole may be provided in the bottom of the decomposing-compartment for the withdrawal of the impurities, such as disintegrated carbon, when it is desired to wash out the cell. Similarly the combining-compartment is provided with openings 8 and 9, the former for the admission of fresh Water and the latter for the withdrawal of the caustic alkali. Provision maybe made in the cover for thewithdrawal of the hydrogen.

'The efficiency of electrolytic cells employing a mercury cathode in this manner is do pendent upon the speed with which the alkali .metal deposited on the surface of the mercury in the decomposing-compartment sides of the troughs can be transferredt-o and re moved from the mercury surfaces in the combining-compartment sides of the troughs.

The richer the amalgam is which is transferred by the stirring below the rim into the decomposing-compartment the greater is its buoyancy in the surrounding mercury, and

1 the more rapidly the alkali metal can be transferred from the mercury in the decomposingcompartment and cleared from the surface of the mercury in the combining-compartment the greater is the current density that can be successfully employed per unit area of mercurysurface. By employing a deep mercury seal and agitating the mercury and amalgam in the manner hereinbefore described I am able to efiect a very rapid transference of the amalgam to the combining-compartment sides of the troughs. At the same time the local action set up by the little carbons j, Fig. 1, causes the decomposition of the amalgam as fast as it is transferred to the combiningcompar'tment sides of the troughs by the action of the stirrers. The increased rapidity of transmission and decomposition of the amalgam thus produced enables me to employ considerably greater current densities per unit area of the mercury surface and to obtain a higher efficiency with this cell than has hitherto been practicable.

A further important advantage obtained by my invention over other existing methods is the very efiective control over the alkali metal deposited on the mercury in the event of the formation of an excess of amalgam there after a protracted period of working. The excess can quickly be cleared by stopping the current which passes through the brine'solution and continuing the agitation of the mercury until the stirrers have transferred the excess of amalgam to the other side of the trough. In order, however, to avoid the formation of hypochlorites, it is preferable to merely diminish the current density instead of entirely stopping the cur rent. The transference of amalgam is very quickly eifected by the stirring, so that the current need only be interrupted or diminished for a short time. The production of caustic alkali is continuous in this case, although the passage of current through the brine is diminished for a short period. Instead of stopping or diminishing the current, however, I may increase the speed at which the stirrers travel, and by this means transfer the excess of amalgam to the other side of the'trough. By any of these means I am always able to eflect in a given time the transference of a greater quantity of amalgain than is formed in that time, and to effect by the occasional use of these means a continuous and efficient working of the cell with the minimum production of hypochlorites.

I may employ my invention in cells which have a very shallow mercury seal and which operate normally by surface-tension effects and difiusion. In this case I slowly stir the mercury in the decomposing-compartment at intervals only. By this means any excess of amalgam formed on the decomposing-compartment side of the trough isperiodically transferred below the rib of the seal to the combining-compartment. The efficiency of the cell is thus considerably increased and steady working insured.

I have made a number of careful experiments with cells employing relatively deep mercury seals and operated in the manner hereinbefore described, and I have found that I can operate the cells under much more unfavorable conditions than should be allowed in practice with a current density of twentyfive amperes at a voltage not exceeding 6.5. It is obvious that at such a high current density as this the transference of the amalgam to the combining-compartment and the removal of alkali metal was exceedingly rapid and effective or the working of the cell would very soon have been interrupted by the formation of solid amalgam in the decomposingcompartment sides of the troughs.

It will be seen that the amount of mercury in the troughs in relation to the exposed area of the mercury is very small; but the area and number of the carbon anodes are made very large in relation to the mercury surface, so that while there is a very high current density per unit area of mercury surface there may be only a very small current density per unit area of carbon. It may indeed be so small that disintegration of the carbon is almost entirely avoided.

Another important feature of this invention is the reduction of the quantity of mercury required per ampere of current. For example, I find it quite practicable with a current density of twenty-five amperes per square decimeter of mercury-surface to employ in continuous working only from fortyeight to sixty grams of mercury per ampere.

The mechanical work done in moving the stirrers is not serious, and it amounts to only a very small percentage of the total electrical. energy supplied to the cell.

In carrying out my invention according to the modification illustrated in Figs. 4C and 5 I provide a metal tank a, preferably circular in form and lined inside with ebonite or some suitable non-conducting material. Within the tank I arrange a series of superimposed circular mercury-troughs 11, thus forming a circular water-tight partition, dividing the tank into aninner combining-compartment andanouterdecomposing-compartment. The lowest trough 36 is formed with a flat base, which rests upon the bottom of the cell; but the other troughs 11 are constructed with enlarged flanges 12 on their inner sides to enable them to be attached by metal bolts or screws 10 10 to a suitable number of conductive uprights 13 13, which stand on the bottom ofthe cell and are tied together by and in metallic contact with an iron cylinder 14:, which is provided with a number of openings 56 to permit the alkaline hydrate to pass freely through them. The troughs and uprights are covered with suitable insulating material; but they are in metallic contact With each other by means of-the screws 10. In order that the mercury in the troughs shall be in electrical contact with the metal of each trough above, small portions of the insulation are removed from the bottoms of the troughs at 15, as seen in Fig. 8. The top trough 17 contains water instead of mercury, and it acts as a water seal for the cover 18 over the combining-compartment. The carbon anodes 9 rest on the bottom of the decomposing-compartment and are held in electrical contact at their tops with a metallic frame 0, which carries the positive terminal 12, the frame 0 being supported upon an insulated cover 21. The outer insulated flange of the cover dips into an insulated water-trough 23, carried by the walls of the cell, and the inner flange dips into a similar water-trough 24, supported by a suitable number of pillars 25, fixed to the bottom of the cell. The electric current entering the cell at the carbon anodes passes through the brine solution to the mercury in the troughs. From the mercury it passes to the troughs at the uninsulated parts 15, Fig. 8, and thence by the screws 10 to the uprights 13 and the cylinder 14. The negative terminal may be connected to these uprights, so that the current leaves the cell by way of the uprights 13 and terminal 26. It will be seen that some of the electric current passes from the surface of the mercury directly to the iron cylinder (which serves as an auxiliary cathode) through the alkalinehydrate solution, and thereby assists in removing the alkali metal from the amalgam. The iron cylinder should be provided with holes 56 to allow free access of the brine solution inside the cylinder to the troughs. Instead of using the iron cylinder 14, however, I prefer to use small pieces of carbon with wire wound around them or pieces of partially-metal-coated carbon or carbon and filings, as hereinbefore described, these special carbons being placed on the surface of the mercury in the combining-compartment to hasten the decomposition of the amalgam. I provide the decomposing-compartment of the cell with a number of rods 27, carrying teeth or stirrers t, projecting into the mercury. The rods are adjustably carried by a circular frame 28, having radial arms 29 and a central boss 31 secured to the vertical shaft 32, the axis of which coincides with the vertical center line of the circular combining compartment. The rods 27 may be tied together at one or more places by hoops 33, the ends of the rods being guided by means of a guide-wheel running upon a beveled rail 34 on the bottom of the cell. The shaft maybe supported above the cell in any well-known ICC manner, and it is rotated slowly, so as to cause the stirrers if to thoroughly agitate the mercury in the troughs, whereby the amalgam is transferred from the decom posing-compartment sides of the troughs to the other sides in the manner hereinbefore described. It may be rotated continuously in one direction, or it may be moved in one direction for a short time, and then the direction may be reversed. An annular cover 22 is fixed to the moving frame and constructed with deep flanges dipping into the water in the troughs 17 and 24, whereby the chlorin is prevented from escaping to the atmosphere. The decomposing compartment is provided with the necessary concentrated brine-inlet pipe 6 and diluted-brine outlet 7. The chlorin may be drawn off by one or more pipes fixed in any suitable part of the cover 21. An additional hole (not shown in the drawings) may be provided in the bottom of the decomposing-compartment for the withdrawal of sediment when the cell is being cleaned out. Fresh water may be admitted to the combiningcompartment by a pipe 37, fixed to the bottom of the cell, and the caustic alkali may be withdrawn from an opening 38, also at the bottom of the cell. A pipe 39 allows the removal of the hydrogen.

In carrying out my invention according to a third modification, as seen in Figs. 6 and 7, I employ an outer tank ct, similar to that described with reference to Figs. 4 and 5. A series of superimposed circular mercurytroughs are also provided, the bottom one beiug similar in form to the bottom trough in the modification described above. The other troughs 20 and 30 are constructed with large inner and outer flanges 41 and 42, respectively, by means of which they are secured to uprights 43 and 44, respectively. The troughs are in metallic contact with the uprights 43 and 44 by means of the screws which pass through the flanges to the uprights. The uprights 43 are attached by screws 49 to a circular frame 45, provided with arms 46 46 and a central boss 47, mounted upon a vertical and rotatable shaft 48, the longitudinal axis of which coincides with the vertical center line of the combining-compartment. The metallic uprights 44 are covered with ebonite and are fixed to the bottom of the cell. An auxiliary cathode consisting of an iron cylinder 14, similar to that employed in the cell described hereinbefore, may be fixed to the uprights 43 by metal screws, by means of which the cylinder and uprights are placed in metallic contact with each other. It will be seen that the troughs 20 20 20 are rotatable with the shaft 48, while the alternate troughs 36, 30, 30, and 17 are fixed. The troughs are covered with insulating material; but in ortions of the bottoms of all the troughs and of the tip of each rib of the fixed troughs uninsulated, as seen at 15 and 51 in Fig. 8. The carbon anodes 'g rest upon the bottom of the cell and are held in electrical contact with a metallic frame 0, which carries the positive terminal 12. An insulated flanged cover 21, through which the anodes pass, closes the top of the decomposing-compartment and prevents the escape of chlorin. The negative terminal is preferably attached to a projection 52, formed in thetop trough 17, which contains water to form a seal for the covers 21 and 18. The current entering the cell by the carbon anodes 9 passes through the brine solution to the mercury in the troughs and leaves the troughs by way of the upright 44 and the projection 52 on the top trough 17..

At the same time a current also passes from the surface of. the mercury in the combiningcompartment through the alkaline-hydrate solution to the iron cylinder 14, whence it re- The iron cylinder thus acts cept the bottom one and dipping into the mercury in the decomposing-compartment side of the troughs below. As the troughs 20 20 20 are rotated by the shaft the vanes 53 stir the mercury in all the troughs. In the case of the fixed troughs the vanes move in relation to the mercury, but in the case of the r0- tatable troughs the mercury moves in relation to the vanes. The effect on the amalgam and mercury is, however, the same in both cases, and the vanes perform the same functions as the teeth t of the stirrers hereinbefore described. The weight of the shaft 48 may be borne by suitable bearings situated above the cell in any well-known manner; but its lower end should enter a guiding-bracket 54 to insure true rotation of the troughs. The rotation of the shaft may be continuously in one direction or it may be frequently reversed. Any suitable and known mechan- 38, and 39 allow the admission of fresh water I and the withdrawal ofthe caustic alkali and hydrogen, respectively, from the combiningcompartment. The blades and vanes of the stirrers, in addition to efiecting the transference of amalgam from one side of the troughs to the other, stir the brine solution, thereby causing the concentrated solution to mix with the diluted solution near the mercurytroughs.

Having now described my invention, what I claim as new, and desire to secure by Letters Patent, is

1. The herein-described process of producing alkali amalgam and separating it to form alkali hydrate which consists in separating the decomposing-cell from the combining-cell by a deep mercury seal, depositing alkali metal by electrolysis upon the mercury in the decomposing-cell, forcing the amalgam from the surface of the mercury in the decomposing-cell deeply into the mercury in opposition to its buoyancy and underthe rib of the seal, allowingthe amalgam to rise by its buoyancy through the mercury in the combiningcompartment and decomposing it on the surface of the mercury there by means of local action, substantially as described.

2. The herein-described process of producing alkali amalgam and separating it to form alkali hydrate which consists in separating the decomposing-cell from the combining-cell by a deep mercury seal, decomposing alkali metal by electrolysis upon the mercury in the decomposing-cell, forcing the amalgam at intervals from the surface of the mercury in the decomposing-cell deeply into the mercury in opposition to its buoyancy and under the rib of the seal, allowing the amalgam to rise by'its buoyancy through the mercury in the combining-compartment and decomposing it on the surface of the mercury there by means of local action, substantially as described.

3. The herein-describedprocess of producing alkali amalgam and separating it to form alkali hydrate which consists in separating the decomposing'cell from the combining-cell by a deep mercury seal, depositing alkali metal by electrolysis upon the mercury in the decomposing-cell, forcing the amalgam from the surface of the mercury in the decomposing-cell deeply into the mercury in opposition to its buoyancy and under the rib of the seal, allowing the amalgam to rise by its buoyancy through the mercury in the combiningcompartment and decomposing it on the surface of the mercury there by placing small pieces of carbon provided with conductive material independent of the amalgam, substantially as described. v

In witness whereof I have hereunto set my hand in presence of two witnesses.

MEYER WILDERMANN. Witnesses:

ALBERT E. PARKER, FRANCIS J. BIGNELL, 

